Field of the Invention
The present invention relates to a method for printing a wood material board and to a wood material board with a printed decorative layer.
Description of Related Art
The use of wood material boards in the furniture industry, as floor coverings or else for cladding walls and ceilings requires machining or finishing the surface of the wood material boards. Normally, in the areas of application mentioned, the wood material boards are coated with a decorative paper. No limits are placed on the variety of variously patterned decorative papers, so that wood material boards having a multiplicity of different decorations, such as stone or wood decorations, can be obtained.
As an alternative to the use of decorative papers on wood material boards, in the past the direct printing of wood material boards has been developed, since the printing of paper and the subsequent lamination or direct coating of the latter onto the wood material board is dispensed with.
The printing techniques primarily used in this case are the gravure printing process and the digital printing process. The gravure printing process is a printing technique in which the elements to be depicted are present as depressions in a printing form, which is inked before the printing. The printing ink is primarily located in the depressions and is transferred to the object to be printed on the basis of contact pressure of the printing form and of adhesive forces. In the case of digital printing, on the other hand, the printing image is transferred directly from a computer into a printing machine, such as a laser printer or inkjet printer. The use of a static printing form is dispensed with.
However, it is possible to foresee that the gravure printing technology will be displaced to an ever greater extent by the digital printing technology. From a cost point of view, this is based on the considerable reduction in costs for digital printers and digital printing inks and, in particular from a technological point of view, on the very great flexibility and the styling possibilities of the digital printing technique, in particular taking into account the trends to increasingly smaller batch sizes.
However, some problems still stand in the way of the complete conversion from gravure printing to digital printing.
Firstly, the production speed of a digital printer is still considerably below that of a modern varnishing line or short-cycle press. These are usually the next value creation stages after the digital printing.
Secondly, there is frequently incompatibility between the digital printing inks used, which can be implemented on a water base, on a UV base or on a solvent base, and the layers to be applied subsequently for the purpose of sealing and for wear protection.
A further aspect is that, during the transport and/or the handling of boards with unprotected decorative prints on the upper side in a production chain, contamination and/or damage to the decoration has to be taken into account. This leads to a reduction in quality but can often only be identified late in the production chain, so that a great deal of effort and high costs follow.
When the gravure printing technique is used in wood material boards based on aqueous printing inks with subsequent finishing by means of varnishing, these problems are obviously not posed, since no productivity differences between printing and varnishing exist and therefore intermediate storage or transport is dispensed with.
The problem already exists in somewhat more pronounced form in the use of wood material boards decorated by gravure printing which are subsequently to be coated with wear protection in a short-cycle press. Here, the productivity of the printing line is already considerably above that of the short-cycle press. Surface protection for transport and/or intermediate storage is therefore absolutely necessary. Such a surface protection is normally applied via a roll application and comprises a formulation which consists of a thermosetting resin, for example melamine resin. In this case, barely any adhesion problems occur, so that technologically there are barely any restrictions.
In the case of a digital print, this is far more complex and more difficult. After the decision for an ink system has been made (e.g. UV-based digital printing ink), in addition to the aforementioned productivity restrictions, in particular incompatibilities in specific processing lines occur. For example, when UV-based digital printing inks are used, subsequent coating with aqueous melamine resins is difficult, which means that further processing in a short-cycle press by using this thermosetting resin generates high technical hurdles.
There is a great need for a technical solution which does not restrict or make more difficult the process steps following the printing operation for the further processing or finishing of wood materials.